PROJECT SUMMARY Alzheimer?s disease (AD) is a complex neurodegenerative condition that affects millions of individuals worldwide and currently has no preventative or disease-modifying therapies. Exciting results from heterochronic parabiosis studies indicate the presence of rejuvenating factors in the circulation that can restore youthful characteristics to aged cells and tissues, including the restoration of aged neural stem activity and cognitive function. Intriguingly, heterochronic parabiosis studies have also shown that exposure of transgenic AD model mice to a young systemic environment results in a marked amelioration of the cognitive deficits and AD-like neuropathology observed in these animals. The beneficial effects of young blood have been observed in multiple transgenic AD models. However, the identities of the blood-borne factors that mediate these effects are still unknown. This proposal is built upon the exciting results emerged from studies funded by R01AG057433, with the goals of identifying and characterizing circulating anti-geronic factors conserved in mammals, including human, bovine, and mouse. We found that systemic administration of one of the top candidate anti-geronic factors, PEDF, significantly improves deficits in cognitive function in aged wild type mice. We hypothesize that conserved circulating anti-geronic factors such as PEDF mediate the rejuvenation effects of young blood in both aged wild type animals and transgenic animal models of AD, and that systemic treatment of these factors to an AD mouse model will improve cognitive function and ameliorate AD-like neuropathology. To test this hypothesis, we will employ the well-studied 5XFAD transgenic mouse model of AD and will investigate whether and to what extent top conserved anti-geronic factors exert beneficial effects on cognitive function and AD-like neuropathology in vivo by measuring changes in amyloid plaque formation, gliosis, synaptic density, cerebrovascular integrity, and cognitive behavior, as compared to vehicle-treated controls. To understand the mechanisms through which these factors exerts protective and restorative effects, we will perform single cell RNA-seq analysis to identify the biological processes and specific cell types mediating their beneficial effects in the brain. Defining the cell type- specific transcriptional programs that are altered in the brain of the 5XFAD mouse model during the progression of AD pathology and how these are affected by treatment with anti-geronic factors will provide mechanistic insights into the protective and restorative effects of youthful blood-borne factors and may identify new therapeutic targets for AD.